Method for making metal-air cell

ABSTRACT

A process for making a metal/air oxygen (air) battery is provided comprising the steps of applying two spaced-apart cathode layers, one adjacent one edge and one generally centrally disposed on one face of an air permeable sheet-form member of electrically conductive material, applying an anode layer on each surface adjacent the other edge of the sheet-form member, applying electrolyte-resistant absorbent material to the outer surfaces of the anode, folding the sheet-form member into a generally S-form configuration and interleaving with another similarly folded sheet-form member so that the two cathode layers which face one another have the anode layers of said other member therebetween and locating an air permeable electrically insulating separator between the adjacent uncoated surfaces of the sheet-form members.

United States Patent Argent et al.

[ 51 Feb. 15, 1972 [54] METHOD FOR MAKING METAL-AIR CELL [72] Inventors:Edwin John Argent, Pyrford, near Woking; Peter J. Gillespie,Basingstoke, both of England [73] Assignee: Energy Conversion Limited,London, En-

gland [22] Filed: Apr. 8, 1969 [21 Appl. No.: 814,367

3373,3176 7/1968 Rosansky 1 36/86 Primary Examiner-Allen B. CurtisAttorney-Morgan, Finnegan, Durham & Pine 57] ABSTRACT A process formaking a metal/air oxygen (air) battery is provided comprising the stepsof applying two spaced-apart cathode layers, one adjacent one edge andone generally centrally disposed on one face of an air permeablesheet-form member of electrically conductive material, applying an anodelayer on each surface adjacent the other edge of the sheet-form member,applying electrolyte-resistant absorbent material to the outer surfacesof the anode, folding the sheetform member into a generally S-formconfiguration and interleaving with another similarly folded sheet-forrnmember so that the two cathode layers which face one another have theanode layers of said other member therebetween and locating an airpermeable electrically insulating separator between the adjacentuncoated surfaces of the sheet-form members.

2 Claims, 2 Drawing Figures METHOD FOR MAKING METAL-AlR CELL Thisinvention relates to electrochemical cells and more particularly tometal/oxygen (air) cells.

In accordance with one aspect of the invention a metal/oxygen (air) cellcomprises a porous anode having applied to at least one surface thereofa layer of electrolyte-resistant absorbent material, catalytic cathodematerial being applied directly to said layer and current leads to saidanode and to a current collector associated with said catalyticmaterial.

Such a cell will operate when an electrolyte is supplied to theabsorbent layer and oxidant (air) is supplied to the cathode. By makingthe various components of relatively cheap materials it becomes economicto throw away the cell after the useful anode material has beenconsumed; the cell is, then, a primary cell which can be made to anydesired size. It is envisaged that this construction will be applicablemore particularly, though not only, to cells of small power, forinstance of the order ofa few watts.

The catalytic material may be sprayed onto the absorbent electrolytelayer or it may be on the current collector that is pressed into thesurface of said layer.

The construction can be used, for example, to form a battery where aplurality of cells are arranged in series. These cells may be formed oneby one as layers, one next to the other, but in this construction it isnecessary to interpose separators between adjacent cells that arepervious to oxidant gas to enable the gas to reach the backs of thecathodes in sufficient quantity to maintain depolarization thereof. Sucha separator may comprise metal wool that is resistant to theelectrolyte; stainless steel wool could form a useful separator.

Alternative separators may comprise nickel or silver wire wools andmetallized plastics wool. Metallic separators have the additionaladvantage of serving as current collectors in contact with the cathodicmaterial and, if the anode is not protected by insulating material, suchas a plastics foil, electrical connection is made with the anode of theadjacent cell, thus serving to connect the cells in series. It ,ispossible to back the anode alternatively with a metal foil, in whichcase the series connection can be made automatically as described. Ifthe outer face of the anode is so protected, connection may still bemade to the cathode by insertion of a current lead into contact with themetallic separator.

The foil backing, whether it be of metal or of plastics material, willserve also to avoid loss of electrolyte through the anode.

lf cells are required to be insulated from adjacent cell it may bedesirable to make the separator of nonmetallic material and for thispurpose a gauze ofplastics material, such as nylon, may be used; thereis a proprietary gauze available, known under the name of Netlon.

Another possibility is to make a battery of bicells in which a seriesconnection between the bicell element is made by wrapping the bicathodein a current connector which is an extension of a current collector ofthe anode of the adjacent element. A nonconducting separator/airpermeator such as Netlon is then required between adjacent elements.

According to another aspect of the invention, there is provided a methodof making a metal/oxygen (air) cell comprising applying a layer ofelectrolyte-resistant absorbent material to at least one surface of aporous anode, applying a catalytic cathode material directly to saidlayer and connecting current leads to said anode and to a currentcollector associated with said catalytic material.

According to a further aspect of the invention there is provided amethod of making a metal/oxygen (air) battery comprising applying twospaced-apart cathode layers one adjacent one edge and one generallycentrally disposed on one face of an air permeable sheet-form member ofelectrically conductive material, applying an anode layer on eachsurface, adjacent the other edge, of the sheet-form member, applyingelectrolyte-resistant absorbent material to the outer surfaces of theanode, folding the sheet-form member to a generally S- formconfiguration and interleaving with a further similarly foldedsheet-form member so that the two cathode layers which face one anotherhave the anode layers of the other member therebetween, an airpermeable, electrically insulating separator being positioned betweenadjacent uncoated surfaces of the sheet-form members.

The sheet-form members may be produced by coating a conductive web andthen cutting the web into separate lengths to produce the sheet-formmembers.

The foregoing and further features of the invention may be more readilyunderstood from the following description of two preferred embodimentsthereof, by way of example, with reference to the accompanying drawing,in which:

FIG. 1 is an end sectional view ofa metal/oxygen (air) cell, and

FIG. 2 is an end sectional view of (air) battery during assembly.

Referring now firstly to FIG. 1 there is shown a metal/oxygen (air) cellcomprising a porous zinc anode 11 which has a layer ofelectrolyte-resistant absorbent material 12 applied directly on onesurface thereof. A cathode 13 comprising catalytic cathode material issprayed or pressed on to the layer 12. The other surface of the anode 11carries a foil 14 to prevent loss of electrolyte; such foil 14 may beelectrically insulating or conductive. An air permeable separator 15,which may be metal or plastics wool, is positioned between the cathode13 and the foil 14 ofthe next adjacent cell. By making the foil 14conductive and the separator 15 of stainless steel wool the cells of abattery are connected in series thereby. Electrolyte for the cell iscontained within the anode 11 and layer 12 and a reservoir (not shown)may also be provided for supplying electrolyte thereto.

Referring now to FIG. 2, there is shown two cells of a metal/oxygen(air) battery during assembly. In this embodiment the separator 15 is ofan electrically insulating material, such as nylon. The anodes 11 do notrequire a foil layer 14 since a layer 12 and cathode 13 are positionedone on each surface of each anode 11. Each cell is electricallyconnected to the next adjacent cell by a conductive lead 16 which passesfrom within the anode 11 of one cell to contact both cathodes 13 of thenext adjacent cell. The lead 16 is a sheet-form member, such as a metalgauze.

This form of battery may be produced by forming the anode 11 on bothsurfaces along one edge of a web of the lead 16. The outer surfaces ofthe anode 11 then have the absorbent layer 12 applied thereto. Thecathodes 13 are applied on one side of the web, one adjacent the otheredge and one spaced therefrom generally centrally of the web. The web isthen cut into separate lengths and bent into generally S-form and thecells assembled into a battery as shown in FIG. 2.

In the types of cell illustrated, it is probable that some form of sealwill be necessary to prevent excessive leakage or evaporation ofelectrolyte from the cell for certain applications where it is notpossible to provide a reservoir of electrolyte. It could be arranged,for example, that some, if not all, of the edges of each cell are sealedaround the anode, cathode and separator and the cell could be encased ina very simple manner in a plastics mounting with the cathode surfaceexposed for access to an oxidant gas. Feeder tubes may be provided forelectrolyte to be fed to the cell and, possibly, replenished.

It is of interest to indicate that a further possible way of preparing acell in accordance with the invention is to wrap a porous metal anode(such as zinc) with a silver gauze current collector in a wrapping ofalkali-resistant asbestos or other heat-resistant separator material.The wrapping is then coated by dipping, painting, spraying or otherwiseapplying an acetone/water dispersion of a hydrophobic agent such asP.T.F.E. polytetrafluoroethylene and a suitable catalyst, such as arelatively cheap high surface area graphite powder. This graphite powdermay be activated by silver or other oxygen reduction catalytic material.The catalyst is then dried, lightly rolled and thereafter cured at about300 C. in a vacuum oven to remove the wetting agent. To improveelectrical contact on a part of a metal/oxygen the cathode catalyst, ametallic powder may be deposited, using conventional methods. Finally, ametal gauze current collector such as nickel, is wrapped round the wholestructure, and this provides sufficient pressure to give electricalcontinuity.

The feasibility of this system has been demonstrated by a single bicellunit which ran for 10 hours at lma./cm. and 1.2 volts full cell voltage,i.e., 66 percent Zinc utilization. It was also capable of supportingcurrents up to 50 ma./cm. at 1 volt.

What is claimed is:

l. A method of making a metal/oxygen (air) battery comprising the steps:

a. applying two spaced-apart cathode layers one adjacent one edge andthe other generally centrally on one face of an air permeable sheet-formmember of electrically conductive material;

b. applying an anode layer on each surface, adjacent the other edge,ofthe sheet-form member;

c. applying electrolyte-resistant absorbent material to the outersurfaces of the anode;

d. folding the sheet-form member to a generally S-form configuration andinterleaving with a further similarly folded sheet-form member so thatthe two cathode layers which face one another have the anode layers ofthe other member therebetween, and

e. positioning an air permeable, electrically insulating separatorbetween adjacent uncoated surfaces of the sheet-form members.

2. A method as claimed in claim 1 wherein the sheet-form members areproduced by coating a web and then cutting the web into separate lengthsto form the sheet-form members.

2. A method as claimed in claim 1 wherein the sheet-form members areproduced by coating a web and then cutting the web into separate lengthsto form the sheet-form members.